Suspicious insects on pupa

[saye]

For months now (+6) I've noticed small insects (compared with the pupa they're apparently carrying their business on) which have sparked two basic questions: 1. What are they (taxonomy/trophic level), and 2. Are they an indication that the pupa is dead, i.e., have they been feeding on its decomposing insides. Though not decisively clear on the low quality pictures, these insects seem to usually appear on the abdominal rings (one per ring is common) and other defining joints of the pupal case (but also under the body); this is the reason why I've imagined they are feeding on the dead body that is accessible only through these leaking locales. Initially, when I first saw them, I also imagined they were feeding on the remainder of the fluids excreted by the pupating larva. Basic reason to presume they are feeding on something? Their numbers have appeared to increase, and with it their appearance in different sizes.

The pupa was on put on soil, taken directly from nowhere specific outside, and subjected to everything that was in it, inside a closed container 13.5 x 6.5cm.

What I'm looking for here the most is: is this an indication that the pupa is dead?

And for anyone who's bell might have rang: yes, it's the M. tiliae pupa from that one other thread.

Photos were taken in succession on March 16th, except the first on the second row, which was on March 17th.

[irisscientist]

Saye,

It is difficult to say from the images, but my guess would be that these additions are 'hypopi', 'hypopus' or 'hypopodes'. These are simply a facultative (i.e. dormant), dispersal stage used for transportation of mites to more favourable/suitable environmental conditions. The mites usually attach themselves to the cuticle of other arthropods for dispersal. In this instance however they appear to have attached themselves to the cuticle of your pupa, which in this instance unfortunately will not help transport them to more favourable conditions. Like I said however, is difficult to confirm from the images attached and this is just my best guess. More info on the Hypopi can be read on pages such as the following:

itp.lucidcentral.org/id/mites/invasive_mite/Invasive_Mite_Identification/key/Major_Mite_taxa/Media/Html/AstigHyp.htm

I hope this helps?


Mark

[saye]

Thank you for the reply Mark, however, here's why I don't think these are mites at all (though unsure of the variation of naked-eye morphology of dormant stages), but insects:

1. Though they appeared flattened from directly above, they have an elongated form
2. The largest are around 3mm long, without antennae (this comes up again), and already large for a mite
3. They have clearly three pairs of legs (though this is not uncommon of immature acari, but never so well developed either)
4. They have highly active and long antennae with which they probe, and lastly
5. They arch their thorax to "interact" with the pupa (bite, I don't know), meaning that they have insectoid morphology (a mite can't separate "head motion" from "thoracic motion", since it has an idiosoma). Sorry I can't get a clear picture of this.

I appreciate that you let me know about hypopi though, of which I knew nothing. Thanks.

[rjb]

Just from the appearance I would have said Springtails class Collembola, maybe family Entomobryidae which can get as large as 6mm. Very few of the Collembola are carnivores, almost all should be feeding on bacteria or decaying material, possibly the exuded fluids. You might compare with images at

bugguide.net/node/view/258365/bgpage

Rick

[saye]

I see. So an hexapod but not actually an insect. Another new group; the similarities are identifiable, maybe it's a match. Further indication that the pupa might have long been dead (which I assume is what you meant with "exuded fluids", and what I imagined, decaying inside the pupal case).

Thanks.

[rjb]

I really know little about springtails but I encounter them by the hundreds in leaf detritus. They seem to prefer moist areas and are driven out by the heat in my Berlese funnel. If the pupa is moister than the surroundings, it is possible the springtails are attracted and are feeding on anything moist. I would not draw the conclusion that the pupa is dead because I know little about springtails or Lepidoptera- I am strictly a Coleoptera guy.
Rick

[saye]

I'd say the pupa is definitely moister than the surroundings, as the soil itself lost its dark colour and suggests dessication. I won't presume the pupa is dead myself, though I have imagined it; the pupal case has retained its colour tones, though I abstain from handling it (some say that a dead pupa feels "mushy", but it's not a "test" I'm keen to perform). Thank you for the help.